Acoustical panels are used for a variety of different purposes and are comprised of an array of different fibers, binders and fillers. Primarily, fibrous panels are made from mineral wool, perlite, cellulosic fibers, fillers and binders.
Panel production utilizes combinations of fibers, fillers, bulking agents, binders, water, surfactants and other additives mixed into a slurry and processed into a panel. Examples of fibers used may include mineral wools, fiberglass, and cellulosic material. Cellulosic material is typically in the form of newsprint. Added fillers may include expanded perlite, brighteners, such as titanium oxide, and clay. Examples of binders used in fibrous panels include starch, latex and reconstituted paper products which link together and create a binding system locking all ingredients into a structural matrix.
Organic binders, such as starch, are often the primary component providing structural adhesion for the panel. Starch is a preferred organic binder because it is relatively inexpensive. For example, panels containing newsprint, mineral wool and perlite can be bound together by starch. Starch imparts both strength and durability to the panel structure, but is susceptible to moisture which can cause the panel to soften and sag. Thus, boards containing starch and cellulose are susceptible to atmospheric moisture, which can lead to the weakening of the panel.
One method used to counter the sagging of acoustical panels is to coat the panels with a formaldehyde resin based coating. When formaldehyde resin based coatings are exposed to moisture or humidity they tend to expand which can prevent sagging. Example formaldehyde resins include melamine formaldehyde, as well as other formaldehyde based resins (phenyl formaldehyde and urea formaldehyde) that can be crosslinked.
Cured formaldehyde resins contain residual methylol end groups that have a high affinity for water and the resin has a flexible crosslink structure that can expand as the coating picks up moisture by virtue of hydrogen bonding. When a formaldehyde resin based coating is applied to the back of an acoustical panel, the coating expands in humid conditions and the force created by the expansion of the back of the panel counteracts the sagging force of gravity. However, formaldehyde resins tend to emit into the atmosphere formaldehyde in the usually thermal curing process. As it is well known, formaldehyde is an environmental irritant.
To control formaldehyde emissions, the addition of formaldehyde reactive materials, such as urea, have been used to scavenge the free formaldehyde. Unfortunately, such small molecule scavengers end cap the reactive groups of the formaldehyde resin, thus preventing significant levels of crosslinking from occurring. As a result, the characteristic highly crosslinked elastic polymer structure is never formed. The resulting coating is weak and will not expand significantly upon exposure to humidity, and therefore the coated panel's resistance to sag is greatly impaired.
One method relating to polymeric formaldehyde scavengers for formaldehyde based resins can be found in U.S. Pat. No. 5,705,537 to Hartman, et al. This patent teaches that protein materials and other formaldehyde scavengers were used to reduce the formaldehyde emission of phenol formaldehyde resole foam in its finished state during customer use at room temperature and not during the foam manufacturing process where organic solvents might also be involved. In the above-mentioned patent, the formaldehyde scavengers are an add-on to the foam before customer use. However, sag and humidity resistance change of the foam due to the presence of the formaldehyde scavengers are of no importance for the above-mentioned patent because the formaldehyde scavengers are a heterogeneous mixture with the foam. In the present invention, the materials are coatings or binders, and not foams, and are totally waterborne. For the present invention, the formaldehyde scavenging occurs throughout the usually thermal curing process of the coatings or binders where the formaldehyde is kinetically energized and much harder to scavenge. In addition, the above-mentioned patent does not comprise natural polyamides like soy protein or any synthetic polyamides like polyacrylamide.